Dear Siobhan and Karl, As far as standard names are concerned, I think we need to go ahead and introduce two new names:
integral_of_sea_ice_temperature_wrt_depth_expressed_as_heat_content; Jm-2 sea_ice_albedo; 1. If a single sea_ice albedo is required and snow cover is to be diagnosed separately, then I think we don't need to introduce the new area_type of snow_free_sea_ice at the moment. As far as CMIP5 output is concerned, it seems we need to re-introduce two saved fields as follows: OImon: Long Name: "Thermal Energy Content of Snow on Sea Ice" Standard Name: thermal_energy_content_of_surface_snow Units: J m-2 cell_methods: "time: mean area: mean where sea-ice" dimensions: longitude latitude time LImon: Long Name: "Thermal Energy Content of Snow on Land" Standard Name: thermal_energy_content_of_surface_snow Units: J m-2 cell_methods: "time: mean area: mean where land" dimensions: longitude latitude time OImon row 39 needs to have the units changed to J m-2 and a standard name of integral_of_sea_ice_temperature_wrt_depth_expressed_as_heat_content. For the sea_ice albedo I think we need: OImon row 23 with a standard name of sea_ice_albedo and cell_methods: "time: mean area: mean where sea_ice" If any further discussion of the CMIP5 output is needed, I suggest that we move it away from the mailing list as it isn't strictly a CF matter now that the standard names are (hopefully) agreed. Best wishes, Alison ------ Alison Pamment Tel: +44 1235 778065 NCAS/British Atmospheric Data Centre Fax: +44 1235 446314 Rutherford Appleton Laboratory Email: [email protected] Chilton, Didcot, OX11 0QX, U.K. > -----Original Message----- > From: Siobhan.O'[email protected] [mailto:Siobhan.O'[email protected]] > Sent: 29 September 2010 08:51 > To: Pamment, Alison (STFC,RAL,SSTD); [email protected] > Cc: [email protected]; [email protected] > Subject: RE: [CF-metadata] CMIP5 cryosphere standard names and standard > CMIP5 output > > HI Alison and Karl, > > I am happy with points 1), 2), 6), 7) and 10) > > The two outstanding ones are the Sea ice thermal energy and bare sea > ice albedo, both of which are flagged for action in the CMIP5 document. > If we can switch the thermal_energy_content_of_snow back on for both > land and sea ice surfaces that would resolve one of the points raised > and as I said it was there for land surface under a different name in > an earlier version of the CMIP5 document. > > > For point 9, I think the best compromise is to have one sea ice albedo > only, which would capture the snow covered period, spring melt > conditions and bare summer conditions as well. > > Best wishes > > Siobhan > > -----Original Message----- > From: [email protected] [mailto:[email protected]] > Sent: Tuesday, 28 September 2010 10:15 PM > To: [email protected]; O'Farrell, Siobhan (CMAR, Aspendale) > Cc: [email protected] > Subject: RE: [CF-metadata] CMIP5 cryosphere standard names > > Dear Jonathan and Siobhan, > > Thank you for your responses. Please see below for an update on the > status of the discussions. > > 1) We are agreed on surface_downward_heat_flux_in_snow (Wm-2). The > CMIP5 > output will use > a cell_methods of "area: mean where land". > > This name is accepted for inclusion in the standard name table. > > 2) Jonathan wrote: > > > > (a) Long name 'Surface Temperature of Sea Ice' with units of K and > the > > > following explanatory comments: 'When computing the time-mean here, > > > the time-samples, weighted by the area of sea ice in the grid cell, > > > are accumulated and then divided by the sum of the weights. Report > as > > > "missing" in regions free of sea ice. Note this will be the > surface > > > > snow temperature in regions where snow covers the sea ice.' > > > > > (b) Long name 'Temperature at Interface Between Sea Ice and Snow' > with > > > units of K and the following explanatory comments: 'When computing > the > > > time-mean here, the time-samples, weighted by the area of > snow-covered > > > sea ice in the grid cell, are accumulated and then divided by the > sum > > > of the weights. Report as "missing" in regions free of snow- > covered > > > > sea ice.' > > > > It seems to me that (a) is surface_temperature for area: where > sea_ice, and (b) is > > sea_ice_surface_temperature for area: where snow_on_sea_ice, in > which > I have invented a > > new area_type. Both are time: mean. > > Siobhan wrote: > > I think Jonathan's sub categories where snow_on_sea_ice and > snow_free_sea_ice approach > > helps here, we definitely want the surface temperature over the ice > portion of the grid > > cell rather than over the whole grid cell (using cell methods). Also > the interface > > temperature between snow and ice is important to account for, as it > is > much warmer than > > the surface temperature due to the thermal insulation on snow so I am > no two worried about > > the case when there is no snow cover but again the snow_on_sea ice > (area type) would help to prevent the confusion. > > Jonathan's approach simplifies these quantities and I'm happy to follow > his suggestion. I think, then, that we are agreed on using the > existing > standard name of surface_temperature for the first quantity and > introducing a new standard name of > sea_ice_surface_temperature; K > for the second. > > This name is accepted for inclusion in the standard name table. > > A new type of snow_on_sea_ice will be added to the area_type table. > > I will check that the CMIP5 output document contains the correct > cell_methods entries for these quantities. > > (Items 3, 4 and 5 are closed). > > 6) Alison wrote: > > > I think we should use the existing standard names of > > rainfall_flux; kg m-2 s-1 > > snowfall_flux; kg m-2 s-1 > > and supply a cell_methods attribute of "area: mean where sea_ice over > > sea" for each of them. > > Jonathan says he agrees. > > Siobhan wrote: > > > It makes sense to separate the water flux from snow and rainfall as > the impact differently on the > > surface using the cell methods would indicate them onto the sea ice > portion of the cell. Some > > rain may penetrate into the ice lattice if it s very porous Jonathan > or contribute to melt ponds in > > the Arctic summer, but I don't know of a sea ice models IN CMIP5 > that sophisticated to allow for > > that effect. > > Sorry, Siobhan, I'm not 100 per cent clear whether you are happy to go > with the names I suggested. The names will certainly allow you to > separate snow and rainfall as per your requirements. > > 7) We are agreed on > tendency_of_sea_ice_amount_due_to_lateral_growth_of_ice_floes; kg m-2 > s-1. > > This name is accepted for inclusion in the standard name table. > > 8) Sea ice thermal energy > > Jonathan wrote: > > > sea_ice_thermal_energy; J > > Is it really J, not J m-2? If J m-2, the phrase heat_content would be > > better, as it would be consistent with the existing name > >integral_of_sea_water_potential_temperature_wrt_depth_expressed_as_hea > t > _content > > (J m-2). If really J, I wonder if we can think of a phrase related to > > heat_content. I am assuming that this quantity relates to > > temperature, but maybe it relates to latent heat content? It would be > > good to be clear about this in the name. > > > > Alison wrote: > > According to the CMIP5 document, the unit is J and the long name is > 'Sea > > Ice Total Heat Content'. The explanation says, 'Ice at 0 Celsius is > > assumed taken to have a heat content of 0 J. When averaging over > time, > > this quantity is weighted by the mass of sea ice. Report as > "missing" > > in regions free of snow on land.' > > > > I find this rather confusing - if it is supposed to be a sea ice > > quantity, then surely it should always be reported as "missing" over > > land and open sea. It doesn't sound as though latent heat is > included. > > I don't think we can call it a 'content' because it isn't a quantity > per > > unit area. Perhaps Siobhan can help to clarify this quantity further. > > Siobhan wrote: > > > Sea ice thermal energy, I am a bit confused on the history on this > one > there were two > > requests originally made in my 2008 document sent To Karl and > circulated through the > > cryosphere community. > > > > The first was > > Snow_thermal_energy_content Snth new Jm-2 month 1 > all > > > > For the land surface component. It was in an earlier version of > Karl's > document (I had > > saved 16/6/2009) but is not in the latest 17/9/2010. > > > > The sea ice heat content was given as > > > > integral_of_sea_ice_temperature_wrt_depth_expressed_as_heat_content > hcice New Jm-2 Month 1 All > > > > > > It looks like they retained the hcice name but changed the units. > > > > So I am puzzled as well, I think it should be Jm-2. > > > > The issue of whether the heat content of the snow over the ice should > be included is highlighted, it is possible, > > but it would be preferable as separate variable, as the thermal > properties are very different form the ice, and it > > could confuse interpretation of result if they were merged into one > effect (Unless you are using the UM, Jonathan > > where the atmosphere model treats the two media as if they are > combined). > > We already have the standard name > thermal_energy_content_of_surface_snow > (J m-2) which, if supplied with the correct cell_methods, would deal > with the first quantity Siobhan mentions. However, I agree that it > doesn't seem to be listed as a separate output in the 17/9/2010 CMIP5 > document. If it is needed for CMIP5, then Karl would be the person to > contact. > > We seem to be in general agreement that the units of the sea_ice > thermal > content should be J m-2, so I will feed that information back to Karl. > A > quantity per unit area can certainly be called a 'content' in standard > names, so in fact the original suggestion of > integral_of_sea_ice_temperature_wrt_depth_expressed_as_heat_content; J > m-2 > would be appropriate and it would fit with Jonathan's comments. Is > this > OK? > > 9) Sea ice albedo > > Siobhan wrote: > > I was bothered that the bare sea ice albedo has been flagged for > > removal, It probably should be total sea > > ice albedo, though in NCAR model bare ice albedo is changeable due to > > black carbon and multi-scattering in > > internal layers. There is a comment on the next page about getting > > albedo from the downwelling and > > upwelling shortwave radiation, but this would not allow for the > > penetration of shortwave radiation into the > > ice. My preference is for total sea ice albedo to be saved. This > will > > allows for the more sophisticate > > schemes to have an areal average of seasonal changes in albedos > across > > thickness categories, snow cover > > properties, melt ponds and now aerosols effects to be analyzed, I > > couldn't find surface albedo being > > saved elsewhere in the CMIP5 document. > > Alison wrote: > > In view of Siobhan's comments I think there is definitely a need to > > agree a name for this quantity. I think that Karl is correct that > > 'surface_albedo' would normally refer to the whole grid cell. It > should > > really be 'sea_ice_albedo'. We could introduce a new name of > > 'sea_ice_albedo_assuming_no_snow' but I'm not sure whether it is > really > > correct to use the "assuming" phrase here. Perhaps it would be more > > accurate to use the existing name 'sea_ice_albedo' and introduce a > new > > area_type of 'snow_free_ice'. I'd welcome opinions on this. > > Jonathan wrote: > > > I think that would be a correct description, yes. This area-type is > the counterpart of > > snow_on_sea_ice which I needed above. I think yours should be > snow_free_sea_ice. > > Siobhan wrote: > > > I still support the need for a sea ice albedos, my comments on > whether > it is total or bare > > still stand, again it should be defined on the sea ice portion of the > grid. Alison's > > suggestion of an area type snow_free_ice could help distinguish it is > bare, but if the snow > > depth is also known, then that would be clearer, though there will be > transition months as > > the ice becomes snow free. > > > > So is one total sea ice albedo sufficient? > > One CF standard name for sea ice albedo is sufficient if it is > essentially the same geophysical quantity for snow covered/bare sea > ice. > Then the only issue is to distinguish between surface types and this is > the role of the area_types. Area types of snow_free_sea_ice and > snow_on_sea_ice would allow you to make that distinction, so I am in > favour of introducing one new standard name of sea_ice_albedo, plus the > new area_types. > > Again regarding CMIP5, Karl would be the person to contact if you wish > to save the albedo for both surface types as currently only the bare > ice > quantity is listed in the output document. The quantity > surface_snow_thickness is listed as an output with a cell_methods of > 'mean where sea'. If you wanted the same quantity saved with a > cell_methods of 'mean where sea_ice' then I think it would be a > separate > output. In practice, would the quantity that is already being saved be > enough to tell you whether the ice is bare? > > 10) We are agreed to use the existing names > surface_downward_x_stress; Pa > surface_downward_y_stress; Pa > and introduce two new standard names > upward_x_stress_at_sea_ice_base; Pa > upward_y_stress_at_sea_ice_base; Pa > (all accompanied by a cell_methods attribute of "area: mean where > sea_ice" for CMIP5.) > > The new names are accepted for inclusion in the standard name table. > > Best wishes, > Alison > > ------ > Alison Pamment Tel: +44 1235 778065 > NCAS/British Atmospheric Data Centre Fax: +44 1235 446314 > Rutherford Appleton Laboratory Email: > [email protected] > Chilton, Didcot, OX11 0QX, U.K. > -- > Scanned by iCritical. -- Scanned by iCritical. _______________________________________________ CF-metadata mailing list [email protected] http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
